Firstly, what I am hooking the amp up to? The pre-amp is based around Rod Elliot's project 88 pre-amp that uses the Burr-Brown OPA2134 op amps. My speakers are also home made using Scan-Speak units, 18W8456 Kevlar bass unit and D2905 treble unit and a 4th order Linkwitz-Riley cross over (Volt air-cored inductors and Expotus capacitors).
The amp itself is built using the SPS-80 switch mode power supply from ColdAmp electronics, set at ± 75v. The mains input is filtered and all connections are gold plated, obviously. The box is just a 2U rack mount case, and looks pretty empty.
Lets start with the silence. Switch off the pre-amp so that the input is shorted and stick an ear into the bass cone. Nothing, not a sound. I guess it would be surprising if there was any mains hum from the ColdAmp PSU, but I have to check that I have switched it on. Yes I have. Ear into the treble unit. OK a bit of hiss and noise, but only with my ear right next to the dome, move away a bit and there is nothing.
OK, so onto the bass. The bass is incredibly deep and solid. Percussion sounds wonderfully tight and precise. Bongos sound especially good and the sound just fills the room. Some of this will be due to the PSU of course, but the solid feel is apparent with rock power chords as well which sound really clearly defined and punchy.
Midrange quality is obvious as soon as someone sings. Listen to Martha Tilstone, Katie Melua or Susanne Vega and the voice just seems to be in the room. The same goes for acoustic guitar, Jack Johnston or similar for example. Every nuance of the plucking or strumming of the strings can be heard.
High frequencies sound very clean and musical, never rough or tiring to listen to. Both electric guitars and violins are really clearly defined and never sound strained.
All in all the amp sounds effortless, whether playing Bach or ZZ Top. Somehow there seems to be more space between the notes, more time to hear everything and no difficulty in separating out instruments. There is a wonderful musicality to the sound, the notes seem to tickle the ears somehow and sometimes you only notice how loud it's turned up because you can't hear someone trying to talk to you!
Cheers Nick H
Nick Humphries of the UK - HPA-LSP400se Stereo Amplifier
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